In state-of-the-art digital cameras or cameras with digital camera backs (hereinafter collectively referred to as backs) having large area sensors, the sensors are based on CCD or CMOS technology. In order to allow fast readout of the data from the image sensor, a multiple-output sensor is used. The multiple outputs give the option of reading the sensor data in parallel, hence at least double the readout speed.
An example is the Leaf Valeo 22 camera back, provided by Creo Inc., Canada, where two image sensor outputs are used in parallel to read the 22-Megapixel sensor. The main concern using this technology is calibrating the differences between the two output signals and the two analog processing means in such a way that no differences will be noticeable in the output image, even when the values are significantly amplified digitally subsequent to the analog processing.
Readout from two outputs of the image sensor can result in two image sections with an offset difference or a gain factor between them. If these are constant for each section, it is relatively easy to correct using calibration pixels placed so that light does not impinge on them. However, in many cases the offset and/or gain varies, depending on the location in the sensor, the sensor temperature and a time-varying factor in the analog readout and processing chain, possibly from very small fluctuations in voltage supply or other electronic and physical variables.
Common stitching algorithms, used in panoramic photography for example, are based on an overlap area between the two adjacent parts of the image. In image sensors with multiple outputs there is no overlap area between the different parts. Rather, the captured image is divided between the multiple outputs along straight division lines, constituting the entire common perimeter of the areas to be stitched. The relatively small number of pixels along these perimeters enhance the probability of stitching errors resulting from noise, a real image line placed on the border, etc.